1. Field of the Invention
This invention relates to a process for the preparation of formaldehyde copolymers.
2. Description of the Prior Art
The process for copolymerizing formaldehyde with a cyclic formal in the gas phase in the presence of boron trifluoride is known (see Japanese Examined Patent Publication No. 43-7554). As is seen in the examples of this patent publication, a copolymer obtained according to this process has a low molecular weight and a poor stability in a basic medium is poor. Accordingly, the copolymer is of little or no practical use.
Japanese Examined Patent Publication No. 44-870 discloses a process in which formaldehyde is copolymerized with a comonomer in the gas phase in the presence of an amine in a rotary reaction vessel. When this process is carried out on an industrial scale, the formed polymer is undesirably deposited onto the wall of the reaction vessel in a short time, and the operation cannot be conducted smoothly.
As means for preventing deposition of the polymer onto the wall of the reaction vessel, there may be considered the use of a self-cleaning type biaxial mixer. As the result of experiments made by us, it has been found that problems arise when formaldehyde is copolymerized with a cyclic formal by using this biaxial mixer. For example, the activity of boron trifluoride or an ether complex thereof used as the catalyst is reduced, the productivity is low, and the stability of the formed copolymer in a basic medium is poor.